This invention relates generally to the field of power supply circuits, and more particularly to a system for causing equal sharing of the load by a plurality of power supplies electrically connected thereto.
It is known in the prior art that it is often advantageous to provide a plurality of power supplies to drive a particular load rather than to design and construct a single power supply for that purpose. These advantages come from several sources, such as being able to utilize readily available components rather than requiring power components that may be unduly expensive or unavailable in the present art. There is an advantage in being able to design and construct standardized individual power supply units that can then be selected and utilized in a number for driving a load under consideration. Also, a margin of safety can be designed into such a system by providing more power supply units then would normally be required in order to accommodate failures in individual supplies. There are of course more and varied detailed advantages in such multiple power supply systems, but prior art systems are not without problems.
It has been common in the prior art systems that involve the use of multiple power supplies to drive a given load, to operate the power supplies in a current limit mode. This mode of operation results in the individual power supplies being operated at their maximum power output capacity, with only one power supply making up the balance of the power required for the particular load. For example, if a particular load had six power supplies coupled to it and the output capacity of four of the power supplies operating at maximum output is not quite sufficient to drive the load, four of the power supplies would be operated at maximum capacity with the balance of the load supplied by the fifth power supply. In such a configuration the sixth power supply would not be operative and would be idle. In such a system, if the load were variable and would increase beyond the capacity of the fifth power supply when added to the four power supplies operating at maximum capacity, the sixth power supply would then be brought into operation to supply the balance of the load. Of course it is apparent that the system must be designed such that the maximum load that can be encountered can be supplied by the number of power supplies available.
It has been found that this type of multiple power supply configuration results in unequal stress on the power supplies since some of the power supplies will be operating at maximum capacity at all times, some of the power supplies will be operative at varying capacities depending upon load requirements, and some of the power supplies may be inoperative for long periods of time. This uneven stress operation tends to result in a higher supply failure rate for those power supplies that are operated at maximum capacity for the greatest length of time. Further, systems of that type exhibit a poor response that can be very disruptive to the load when a power supply that is supplying current to the load fails.